Basis: Section 32.1-164.9 of the Code of Virginia
mandates the Board of Health to promulgate regulations for physical
construction, design, and installation of chamber and bundled expanded
polystyrene systems. Additionally, the board is authorized pursuant to §
32.1-12 of the Code of Virginia to promulgate and enforce regulations. Section
32.1-164 of the Code of Virginia authorizes the board to promulgate regulations
governing the collection, conveyance, transportation, treatment, and disposal
of sewage by onsite sewage systems to protect public health, surface water, and
groundwater.

Purpose: The need for the proposed regulation is to
implement § 32.1-164.9 of the Code of Virginia and incorporate
requirements for gravelless material and drip dispersal. The amendments include
construction, design, and installation requirements for gravelless material and
drip dispersal systems. Since 2002, the Virginia Department of Health (VDH) has
recognized, through policies, that gravelless material is an acceptable means
of dispersing effluent. VDH has recognized, through policies, that drip
dispersal is an acceptable means of transmitting effluent. The goal of the
proposed regulation is to permanently add the construction, design, and
installation standards for gravelless material and drip dispersal. The
regulations are essential in order to comply with the provisions of the Code of
Virginia and protect the health, welfare, and safety of the public.

4. Criteria for determining the minimum absorption area
required when utilizing gravelless material;

5. Criteria for the substitution of gravelless material in
place of gravel for gravity percolation lines and low pressure distribution
systems;

6. Specifications for the physical construction of drip
dispersal system components;

7. Minimum requirements for the design of drip dispersal
systems; and

8. Minimum installation requirements for drip dispersal
systems.

Minor clarifying changes to the proposed amendments from the
emergency regulation, published in 30:11 VA.R. 1576 January 27, 2014, are made,
including the following: (i) the term "soil gravel or sand interface"
used in 12VAC5-610-920 and 12VAC5-610-950 A is modified to ensure inclusion of
gravelless material and drip dispersal, and (ii) the proposed regulation establishes
minimum physical construction, design, and installation requirements for
gravelless material and drip dispersal.

Issues: The proposed regulation poses no disadvantage to
the public or the Commonwealth. The proposed revisions permanently incorporate
the emergency regulations for gravelless material and drip dispersal. The
proposed regulations provide a benefit to the public by providing a clear
regulation for use of gravelless material and drip dispersal.

Department of Planning and Budget's Economic Impact Analysis:

Summary of the Proposed Amendments to Regulation.

Pursuant to Chapter 202 of the 2013 Acts of Assembly, the Board
of Health (Board) proposes to incorporate requirements for the use of
gravelless material1 and drip dispersal2 in onsite sewage
systems in this regulation. The legislation specifies that the regulations
shall include the following requirements:

v) Criteria for determining the minimum area requirements
for chamber and bundled expanded polystyrene effluent distribution system
absorption trenches; and

vi) Such other requirements pertaining to the promulgation
of chamber and bundled expanded polystyrene effluent distribution system
regulations for onsite sewage systems as may be deemed necessary by the Board.

The Board's proposed regulatory amendments include these
requirements and criteria.

Result of Analysis. The benefits likely exceed the costs for
all proposed changes.

Estimated Economic Impact. Since 2002, the Virginia Department
of Health (VDH) has approved through policies gravelless material as an
acceptable means of dispersing effluent. VDH has also approved through policies
drip dispersal as an acceptable means of transmitting effluent. The Board's
proposed requirements, specifications, and criteria are similar to those set by
VDH in practice; although there are some differences. Placing the requirements,
specifications, and criteria in regulation will be beneficial in that it will
increase clarity for the public.

In practice VDH has required a $100,000 letter of credit and a
5-year limited warranty from manufacturers for approval of use of their
gravelless (i.e., plastic) systems. VDH believes that the 5-year limited
warranty has not been a binding constraint. In other words, it is consistent
with what the manufacturers offer anyway. In the 15 plus years that this
program has existed, there have been no instances where there has been a need
to access any of these letters of credit to pay for failed manufactured
product.

Under the proposed regulations, neither the letter of credit
nor the warranty will be required. There are currently five manufacturers who
have approved gravelless systems, and consequently each hold a $100,000 letter
of credit. Manufacturers will save the cost of maintaining the letter of
credit, approximately $3,250 per year per firm, under the proposed regulations.

In practice VDH has allowed up to 50% reduction in drainage
field while using gravelless system, but required an informed consent form
signed by homeowner. Under the proposed regulation the drainage field can be
reduced by at most 25%, but no signature from the homeowner is required.

Businesses and Entities Affected. The proposed amendments may
affect applicants for onsite sewage system construction permits and businesses
providing services related to onsite sewage systems; onsite soil evaluators,
professional engineers, onsite sewage system installers, and product
manufacturers. Applicants and service providers are only affected when
gravelless material or drip dispersal components are selected.

In calendar year 2013, VDH processed approximately 13,000
applications. The agency estimates that there are approximately 400 licensed
individuals providing site evaluation and design services for onsite sewage
systems. Additionally, there are approximately 215 individuals licensed to
install onsite sewage systems. The vast majority of these service providers are
small businesses. There are also 5 potentially affected manufacturers.

Projected Impact on Employment. The proposed amendments are
unlikely to significantly affect employment.

Effects on the Use and Value of Private Property. The proposed elimination
of the letter of credit requirement will save manufacturers approximately
$3,250 per year.

Small Businesses: Costs and Other Effects. The proposed
elimination of the letter of credit requirement will reduce costs for small
manufacturers of products used to disperse effluent within the absorption
trench of an onsite sewage system without the use of gravel.

Small Businesses: Alternative Method that Minimizes Adverse
Impact. The proposed amendments will not adversely affect small businesses.

Real Estate Development Costs. The proposed amendments are
unlikely to significantly affect real estate development costs.

Legal Mandate.

General: The Department of Planning and Budget (DPB) has
analyzed the economic impact of this proposed regulation in accordance with
§ 2.2-4007.04 of the Code of Virginia and Executive Order Number 17
(2014). Section 2.2-4007.04 requires that such economic impact analyses
determine the public benefits and costs of the proposed amendments. Further the
report should include but not be limited to:

• the projected number of businesses or other entities to
whom the proposed regulatory action would apply,

• the identity of any localities and types of businesses
or other entities particularly affected,

• the projected number of persons and employment positions
to be affected,

• the projected costs to affected businesses or entities
to implement or comply with the regulation, and

• the impact on the use and value of private property.

Small Businesses: If the proposed regulatory action will have
an adverse effect on small businesses, § 2.2-4007.04 requires that such
economic impact analyses include:

• an identification and estimate of the number of small
businesses subject to the proposed regulation,

• the projected reporting, recordkeeping, and other
administrative costs required for small businesses to comply with the proposed
regulation, including the type of professional skills necessary for preparing
required reports and other documents,

• a statement of the probable effect of the proposed
regulation on affected small businesses, and

• a description of any less intrusive or less costly
alternative methods of achieving the purpose of the proposed regulation.

Additionally, pursuant to § 2.2-4007.1, if there is a
finding that a proposed regulation may have an adverse impact on small
business, the Joint Commission on Administrative Rules is notified at the time
the proposed regulation is submitted to the Virginia Register of Regulations
for publication. This analysis shall represent DPB's best estimate for the
purposes of public review and comment on the proposed regulation.

_________________________________________________

1Gravelless Material means a proprietary product
specifically manufactured to disperse effluent within the absorption trench of
an onsite sewage system without the use of gravel. Gravelless material may
include chamber, bundled expanded polystyrene, and multi-pipe systems.

2Drip Dispersal means an onsite sewage system that
applies wastewater in an even and controlled manner over an absorption area.
Drip dispersal components may include treatment components, a flow equalization
pump tank, a filtration system, a flow measurement method, supply and return
piping, small diameter pipe with emitters, air/vacuum release valves,
redistribution controls, and electromechanical components or controls.

Agency's Response to Economic Impact Analysis: The
Virginia Department of Health concurs with the Department of Planning and
Budget's economic impact analysis. The benefits of the regulations likely
exceed the costs for all of the proposed changes.

Summary:

The amendments permanently incorporate the requirements for
gravelless material and drip dispersal established by emergency regulation
(30:11 VA.R. 1576 January 27, 2014) pursuant to Chapter 202 of the 2013 Acts of
Assembly, which required the State Board of Health to promulgate regulations
for chamber and bundled expanded polystyrene effluent systems. The board may
promulgate regulations for other distribution technologies. The Sewage Handling
and Disposal Regulations (12VAC5-610) contain construction, design, and
installation requirements for gravel and pipe effluent absorption trench, low
pressure distribution, elevated sand mound, and sand-on-sand systems. The
amendments establish construction, design, and installation requirements for
gravelless material and drip dispersal systems, as follows:

4. Criteria for determining the minimum absorption area
required when utilizing gravelless material;

5. Criteria for the substitution of gravelless material in
place of gravel for gravity percolation lines and low pressure distribution
systems;

6. Specifications for the physical construction of drip
dispersal system components;

7. Minimum requirements for the design of drip dispersal
systems; and

8. Minimum installation requirements for drip dispersal
systems.

Minor revisions for clarification, based on public comment,
were made to the emergency regulation for the proposed amendments. In
12VAC5-610-955 B 6 a requirement that the system design protect from siphoning or
backflow was added. In 12VAC5-610-995 C 3, general parameters for loading rates
for sloping absorption areas were made specific requirements.

This chapter is supplemental to the current Virginia
Sewerage Regulations, or their successor, which were adopted jointly by the
State Board of Health and the Department of Environmental Quality pursuant to §
62.1-44.19 of the Code of Virginia. This chapter addresses the handling and
disposal of sewage not regulated by a Virginia Pollutant Discharge Elimination
System (VPDES) Permit.

A. This chapter addresses the handling and disposal of
those portions of sewage flows not regulated by a Virginia Pollutant Discharge
Elimination System (VPDES) Permit or a Virginia Pollutant Abatement (VPA)
Permit issued in accordance with 9VAC25-31 or 9VAC25-32, respectively.

B. Reclamation and reuse of sewage may be subject to
permitting by the Department of Environmental Quality under 9VAC25-740.

The term distribution methods refers to the piping, flow
splitting devices, gravel, and other appurtenances beginning at the point of
flow splitting and ending at the soil-gravel or sand interfaceapplication
of effluent to the soil absorption area. Two basic methods are considered:

Gravity distribution is the conveyance of effluent from a
distribution box through the percolation lines at less than full flow
conditions. Flow to the initial distribution box may be initiated by pump,
siphon or gravity.

A. Enhanced flow distribution. Enhanced flow distribution is
the initiation of the effluent flow to the distribution box by pump or siphon
for the purpose of assuring more uniform flow splitting to the percolation
lines. Enhanced flow distribution shall be provided on systems where the flow
is split more than 12 times or the system contains more than 1200 linear feet
of percolation lines. For the purpose of this chapter, enhanced flow
distribution is considered to produce unsaturated soil conditions.

B. System size. Distribution systems containing 1800 or more
linear feet of percolation piping shall be split into multiple systems
containing a maximum of 1200 linear feet of percolation piping per system.

C. Distribution boxes. The distribution box is a device for
splitting flow equally by gravity to points in the system. Improperly installed
distribution boxes are a cause for absorption field malfunction.

1. Materials. The preferred material for use in constructing
distribution boxes is concrete (3000 psi). Other materials may be considered on
a case-by-case basis. All materials must be resistant to both chemical and
electrolytic corrosion and must have sufficient structural strength to contain
sewage and resist lateral compressive and bearing loads.

2. Design. Each distribution box shall be designed to split
the influent flow equally among the multiple effluent ports. All effluent ports
shall be at the same elevation and be of the same diameter. The elevation of
the effluent ports shall be at a lower elevation than the influent port. The
placement of the influent ports shall be such as to prevent short circuiting
unless baffling is provided to prevent short circuiting. The minimum inside
width of a gravity flow distribution box shall be equal to or greater than 12
inches. The inside bottom shall be at least four inches below the invert of the
effluent ports and at least five inches below the invert of the influent port.
A minimum of eight inches freeboard above the invert of the effluent piping
shall be provided. The distribution box shall be fitted with a watertight,
removable lid for access.

3. Installation. The hole for placement of the distribution
box shall be excavated to undisturbed soil. The distribution box shall be
placed in the excavation and stabilized. The preferred method of stabilizing
the distribution box is to bond the distribution box to a four inch poured in
place Portland cement concrete pad with dimensions six inches greater than the
length and width dimensions of the distribution box. The box shall be
permanently leveled and checked by water testing. Conduits passing through the
walls of a distribution box shall be provided with a water stop.

D. Lead or header lines. Header or lead lines are watertight,
semirigid or rigid lines that convey effluent from a distribution box to
another box or to the percolation piping.

1. Size. The lead or header lines shall have an internal
diameter of four inches.

2. Slope. Minimum slope shall be two inches per 100 feet.

3. Materials. The lead or header lines shall have a minimum
crush strength of 1500 pounds per foot and may be constructed of cast iron,
plastic, vitrified clay or other material resistant to the corrosive action of
sewage.

4. Appurtenances.

a. Joints. Lead or header lines shall have joints of the
compressions type with the exception of plastic lead or header lines which may
be welded sleeve, chemically fused or clamped (noncorrosive) flexible sleeve.

b. Adapters. Joining of lead or header lines of different size
and/or material shall be accomplished by use of a manufactured adapter
specifically designed for the purpose.

c. Valves. Valves shall be constructed of materials resistant
to the corrosive action of sewage. Valves placed below ground level shall be
provided with a valve box and a suitable valve stem so that it may be operated
from the ground surface.

5. Construction.

a. Bedding. All lead or header lines shall be bedded to supply
uniform support and maintain grade and alignment along the length of the lead
or header lines. Special care shall be taken when using semirigid pipe.

b. Backfilling and tamping. Lead and header lines shall be
backfilled and tamped as soon as possible after the installation of the lead or
header lines has been approved. Material for backfilling shall be free of large
stones and debris.

6. Termination. Header or lead lines shall extend for a
minimum distance of two feet into the absorption trenches.

E. Gravity percolation lines. Gravity percolation lines are
perforated or open joint pipes that are utilized to distribute the effluent
along the length of the absorption trenches.

1. Size. All gravity percolation lines shall have an internal
diameter of four inches.

2. Slope. The slope of the lines shall be uniform and shall
not be less than two inches or more than four inches per 100 feet.

3. Design. Effluent shall be split by the distribution system
so that all gravity percolation lines installed shall receive an equal volume
of the total design effluent load per square foot of trench, i.e., the fraction
of the flow received by each percolation line divided by the length of the gravity
percolation lines shall be equal for all gravity percolation lines in a system.

b. Perforated plastic drainage tubing. Perforated plastic
drainage tubing shall meet ASTM standards. At not greater than 10 feet
intervals the pipe shall be plainly marked, embossed or engraved thereby
showing the manufacturer's name or hallmark and showing that the product meets
a bearing load of 1,000 lb. per foot. In addition, a painted or other clearly
marked line or spot shall be marked at not greater than 10 feet intervals to
denote the top of the pipe.

The tubing shall have three holes, 1/2 to 3/4 inch in diameter
evenly spaced and placed within an arc of 130 degrees, the center hole being
directly opposite the top marking.

Spacing of each set of three holes shall be at four inch
intervals along the tube. If there is any break in the continuity of the
tubing, an appropriate connection shall be used to join the tubing.

6. Installation

a. Crushed stone or gravel. Clean gravel or crushed stone
having a size range from 1/2 inch to 1-1/2 inches shall be utilized to bed the
gravity percolation lines.

Minimum depth of gravel or crushed stone beneath the
percolation lines shall be six inches. Clean course silica sand (does not
effervesce in presence of dilute hydrochloric acid) may be substituted for the
first two inches (soil interface) of the requirerequired six
inches of gravel beneath the percolation lines. The absorption trench shall be
backfilled to a depth of two inches over the gravity percolation lines with the
same gravel or crushed stone. Clean sand, gravel or crushed stone shall be free
of fines, clay and organic materials.

b. Grade boards and/or stakes. Grade boards and/or stakes
placed in the bottom or sidewalls of the absorption trench shall be utilized to
maintain the grade on the gravel for placement of the gravity percolation
lines. Grade stakes shall not be placed on centers greater than 10 feet.

c. Placement and alignment. Perforated gravity percolation
piping shall be placed so that the center hole is in the horizontal plane and
interfaces with the minimum six inches of graded gravel. When open joint piping
is utilized the upper half of the top of the 1/4-inch open space shall be
covered with tar paper or building paper to block the entrance of fines into
the pipe during the backfilling operation. All gravity percolating piping shall
be placed in the horizontal center of the absorption trench and shall maintain
a straight alignment and uniform grade.

d. Backfilling. After the placement of the gravity percolation
piping the absorption trench shall be backfilled evenly with crushed stone or
gravel to a depth of two inches over the piping. Untreated building paper,
or other suitable material shall be placed at the interface of the gravel and
soil to prevent migration of fines to the trench bottom. The remainder of the trench
shall be backfilled with soil to the ground surface.

F. Gravelless material is a proprietary product
specifically manufactured to disperse effluent within the absorption trench of
an onsite sewage system without the use of gravel. Gravelless material may
include chamber, bundled expanded polystyrene, and multi-pipe systems. The
division shall maintain a list of all generally approved gravelless material.
Gravelless material on the generally approved list may be used in accordance
with Table 5.4 of 12VAC5-610-950.

1. Gravelless material that received general approval as of
December 12, 2013, shall retain such status when used in accordance with the
requirements of this chapter. After December 12, 2013, the division shall
review and evaluate new applications for general approval pursuant to the
requirements of this chapter.

a. Any manufacturer of gravelless material may submit an
application for general approval to the division using a form provided by the
division. A complete application shall include the manufacturer's contact
information, product specifications, product approvals in other states or
territories, installation manual, and other information deemed necessary by the
division to determine compliance with this chapter.

b. The manufacturer of gravelless material shall identify
in the application for general approval any recommendation that deviates from
the requirements of this chapter. If the recommendation is approved by the
division, then the manufacturer shall include the deviation in the gravelless
material's installation manual.

2. Gravelless material shall have the following minimum
characteristics for general approval:

a. The minimum exterior width shall be at least 90% of the
total width of the absorption trench. The exterior width of a chamber system
shall be measured at the edge or outer limit of the product's contact with the
trench bottom unless the division determines a different measurement is
required based on the gravelless material's design. The exterior width of
bundled expanded polystyrene and multi-pipe systems shall be measured using the
outside diameter of the bundled gravelless material unless the division
determines a different measurement is required based on the gravelless
material's design. The division shall establish the exterior width of any
gravelless material that is not considered a chamber, bundled expanded
polystyrene, or multi-pipe system.

b. Gravelless material shall have a minimum height of eight
inches to provide a continuous exchange of air through a permeable interface.

c. Gravelless material shall have a permeable interface
that shall be located along the trench bottom and trench sidewalls within the
absorption trench.

e. Gravelless material shall pose no greater risk to
surface water and groundwater quality than gravel in absorption trenches.
Gravelless material shall be constructed to maintain structural integrity such
that it does not decay or corrode when exposed to effluent.

f. Gravelless material shall have a minimum load rating of
H-10 or H-20 from the American Association of State Highway and Transportation
Officials or equivalent when installed in accordance with the manufacturer's
specifications and minimum specified depth of cover in non-traffic or traffic
areas, respectively.

3. For designs using gravelless material, the absorption
trenches shall receive an equal volume of effluent per square foot of trench.
Trench bottom area shall be equal to or greater than the minimum area
requirements contained in Table 5.4 of 12VAC5-610-950. Trench sidewall shall
not be included when determining minimum area requirements. When open-bottom
gravelless material is utilized, it shall provide a splash plate at the inlet
of the trench or other suitable method approved by the manufacturer to reduce
effluent velocity.

4. Installation of gravelless material shall comply with
this chapter unless the department grants a deviation pursuant to
12VAC5-610-660 or the division has granted a deviation identified in the
installation manual.

5. Gravelless material shall contain a pressure percolation
line along the entire length of the trench when low pressure distribution is
utilized pursuant to 12VAC5-610-940 D.

6. When pumping effluent to overcome gravity, any
open-bottom gravelless material shall provide a high-flow splash plate at the
inlet of the trench or other suitable method approved by the manufacturer to
reduce effluent velocity.

7. When enhanced flow distribution is used, open-bottom
gravelless material shall contain a percolation pipe that extends a minimum of
10 feet from the trench's intersection with the header line. The percolation
pipe shall be installed in accordance with the manufacturer's approved
installation manual. The dosing volume shall be a minimum 39 gallons per 100
linear feet of absorption trench.

8. Gravelless material may be substituted for gravel in
accordance with this chapter, provided that the certifying licensed
professional engineer or onsite soil evaluator approves the substitution. The
certifying licensed professional engineer or onsite soil evaluator shall
identify the substitution on the inspection report submitted in accordance with
12VAC5-610-330. A new construction permit pursuant to 12VAC5-610-310 is not
required for the substitution.

Low pressure distribution is the conveyance of effluent
through the pressure percolation lines at full flow conditions into the
absorption area with the prime motive force being a pump or siphon. Low
pressure systems are limited to a working pressure of from one to four feet of
head at the distal end of the pressure percolation lines. For the purpose of
this chapter low pressure distribution is considered to provide unsaturated
soil conditions.

A. Dosing cycle. Systems shall be designed so that the
effluent volume applied to the absorption area per dosing cycle is from seven
to 10 times the volume of the distribution piping, however, the volume per
dosing cycle should not result in a liquid depth in the absorption trench
greater than two inches.

B. Manifold lines. Manifold lines are watertight lines that
convey effluent from the initial point of flow splitting to the pressure
percolation lines.

1. Size. The manifold line shall be sized to provide a minimum
velocity of two feet per second and a maximum velocity of eight feet per
second.

2. Materials. All pipe used for manifolds shall be of the
pressure type with pressure type joints.

3. Bedding. All manifolds shall be bedded to supply uniform
support along its length.

4. Backfilling and tamping. Manifold trenches shall be
backfilled and tamped as soon as possible after the installation of the
manifold has been approved. Material for backfilling shall be free of large
stones and debris.

5. Valves. Valves for throttling and check valves to prevent
backflow are required wherever necessary. Each valve shall be supplied with a
valve box terminating at the surface.

C. Pressure percolation lines. Pressure percolation lines are
perforated pipes utilized to distribute the flow evenly along the length of the
absorption trench.

3. Hole placement. Center to center hole separation shall be
between three and five feet.

4. Line length. Maximum line length from manifold should not
exceed 50 feet.

5. Percent flow variation. Actual line size, hole size and
hole separation shall be determined on a case-by-case basis based on a maximum
flow variation of 10% along the length of the pressure percolation lines.

6. Materials and construction. The preferred material is
plastic, either PVC or ABS, designed for pressure service. The lines shall have
burr free and counter sunk holes (where possible) placed in a straight line
along the longitudinal axis of the pipe. Joining of pipes shall be accomplished
with manufactured pressure type joints.

7. Installation.

a. Crushed stone or gravel. Clean gravel or crushed stone
having a size range from 1/2 inch to 3/4 inch shall be utilized to bed the
pressure percolation lines. Minimum depth of gravel or crushed stone beneath
the percolation lines shall be 8-1/2 inches. Clean course silica sand (does not
effervesce in the presence of dilute hydrochloric acid) may be substituted for
the first two inches (soil interface) of the required 8-1/2 inches of gravel
beneath the pressure percolation lines. The absorption trench shall be
backfilled to a depth of two inches over the pressure percolation lines with
the same gravel or crushed stone. Clean sand, gravel or crushed stone shall be
free of fines, clay and organic materials.

b. Grade boards and/or stakes. Grade boards and/or stakes
placed in the bottom or sidewalls of the absorption trench shall be utilized to
maintain the gravel level for placement of the pressure percolation lines. Grade
stakes shall not be placed on centers greater than 10 feet.

c. Placement and alignment. Pressure percolation lines shall
be placed so that the holes face vertically downward. All pressure percolation
piping shall be placed at the same elevation, unless throttling valves are
utilized, and shall be level. The piping shall be placed in the horizontal
center of the trench and shall maintain a straight alignment. Normally the
invert of the pressure percolation lines shall be placed 8-1/2 inches above the
trench bottom. However, under no circumstance shall the invert of the pressure
percolation lines be placed closer than 16-1/2 inches to the seasonal water
table as defined in 12VAC5-610-950 A 312VAC5-610-470 D. When the
invert of the pressure percolation lines must be placed at an elevation greater
than 8-1/2 inches above the trench bottom, landscaping over the absorption area
may be required to provide the two inches of gravel and six inches of fill over
the pressure percolation lines required in subdivision 7 a of this subsection.

d. Backfilling. After the placement of the pressure
percolation piping the absorption trench shall be backfilled evenly with
crushed stone or gravel to a depth of two inches over the opening. Untreated
building paper or other suitable material shall be placed at the interface of
the gravel and soil to prevent migration of fines to the trench bottom. The
remainder of the trench shall be backfilled with soil to the ground surface.

8. Appurtenances. The distal (terminal) end of each pressure
percolation lines shall be fitted with a vertical riser and threaded cap
extending to the ground surface. Systems requiring throttling valves will be
supplied with couplings and threaded riser extensions at least four feet long
so that the flow may be adjusted in each line.

D.Gravelless material with general approval may be
used for low pressure distribution in accordance with the manufacturer's
approved installation manual, Table 5.4 of 12VAC5-610-950, and the applicable
requirements of this chapter.

A. The absorption area is the undisturbed soil medium beginning
at the soil gravel or sand interface which is utilized for absorption of
the effluent. The absorption area includes the infiltrative surface in the
absorption trench and the soil between and around the trenches when trenches
are used.

B. Suitability of soil horizon. The absorption trench bottom
shall be placed in the soil horizon or horizons with an average estimated or
measured percolation rate less than 120 minutes per inch. Soil horizons are to
be identified in accordance with 12VAC5-610-480. The soil horizon must meet the
following minimum conditions:

1. It shall have an estimated or measured percolation rate
equal to or less than 120 minutes per inch.

2. The soil horizon or horizons shall be of sufficient
thickness so that at least 12 inches of absorption trench sidewall is exposed
to act as an infiltrative surface; and

3. If no single horizon meets the conditions in subdivision 2
of this subsection, a combination of adjacent horizons may be utilized to
provide the required 12-inch sidewall infiltrative surface. However, no horizon
utilized shall have an estimated or measured percolation rate greater than 120
minutes/inch.

C. Placement of absorption trenches below soil restrictions.
Placement of the soil absorption trench bottom below soil restrictions as
defined in 12VAC5-610-490 D, whether or not there is evidence of a perched
water table as indicated by free standing water or gray mottlings or
coloration, requires a special design based on the following criteria:

1. The soil horizon into which the absorption trench bottom is
placed shall be a Texture Group I, II or III soil or have an estimated or
measured percolation rate of less than 91 minutes per inch.

2. The soil horizon shall be a minimum of three feet thick and
shall exhibit no characteristics that indicate wetness on restriction of water
movement. The absorption trench bottom shall be placed so that at least two
feet of the soil horizon separates the trench bottom from the water table
and/or rock. At least one foot of the absorption trench side wall shall
penetrate the soil horizon.

3. A lateral ground water movement interceptor (LGMI) shall be
placed upslope of the absorption area. The LGMI shall be placed perpendicular to
the general slope of the land. The invert of the LGMI shall extend into, but
not through, the restriction and shall extend for a distance of 10 feet on
either side of the absorption area (See 12VAC5-610-700 D 3).

1. Required area. The total absorption trench bottom area
required shall be based on the average estimated or measured percolation rate
for the soil horizon or horizons into which the absorption trench is to be
placed. If more than one soil horizon is utilized to meet the sidewall
infiltrative surface required in subsection B of this section, the absorption
trench bottom area shall be based on the average estimated or measured percolation
rate of the "slowest" horizon. The trench bottom area required in
square feet per 100 gallons (Ft²/100 Gals) of sewage applied for various soil
percolation rates is tabulated in Table 5.4. The area requirements are based on
the equation:

log y = 2.00 + 0.008 (x)

where y = Ft²/100 Gals

x = Percolation rate in minutes/inch

Notwithstanding the above, the minimum absorption area for
single family residential dwellings shall be 400 square feet.

2. Area reduction. See Table 5.4 for percent area
reduction when gravelless material or low pressure distribution is
utilized. A reduction in area shall not be permitted when flow diversion is
utilized with low pressure distribution. When gravelless material is
utilized, the design width of the trench shall be used to calculate minimum
area requirements for absorption trenches.

E. Minimum cross section dimensions for absorption trenches.

1. Depth. The minimum trench sidewall depth as measured from
the surface of the mineral soil shall be 12 inches when placed in a landscape
with a slope less than 10%. The installation depth shall be measured on the
downhill side of the absorption trench. When the installation depth is less
than 18 inches, the depth shall be measured from the lowest elevation in the
microtopography. All systems shall be provided with at least 12 inches of cover
to prevent frost penetration and provide physical protection to the absorption
trench; however, this requirement for additional cover shall not apply to
systems installed on slopes of 30% or greater. Where additional soil cover must
be provided to meet this minimum, it must be added prior to construction of the
absorption field, and it must be crowned to provide positive drainage away from
the absorption field. The minimum trench depth shall be increased by at least
five inches for every 10% increase in slope. Sidewall depth is measured from
the ground surface on the downhill side of the trench.

2. Width. All absorption trenches utilized with gravity
distribution shall have a width of from 18 inches to 36 inches. All absorption
trenches utilized with low pressure distribution shall have a width of eight
inches to 24 inches.

F. Lateral separation of absorption trenches. The absorption
trenches shall be separated by a center to center distance no less than three
times the width of the trench for slopes up to 10%. However, where trench
bottoms are two feet or more above rock, pans and impervious strata, the
absorption trenches shall be separated by a center to center distance no less
than three times the width of the trench for slopes up to 20%. The minimum
horizontal separation distance shall be increased by one foot for every 10%
increase in slope. In no case shall the center to center distance be less than
30 inches.

G. Slope of absorption trench bottoms.

1. Gravity distribution. The bottom of each absorption trench
shall have a uniform slope not less than two inches or more than four inches
per 100 feet.

2. Low pressure distribution. The bottom of each absorption
trench shall be uniformly level to prevent ponding of effluent.

H. Placement of absorption trenches in the landscape.

1. The absorption trenches shall be placed on contour.

2. When the ground surface in the area over the absorption
trenches is at a higher elevation than any plumbing fixture or fixtures, sewage
from the plumbing fixture or fixtures shall be pumped.

I. Lateral ground water movement interceptors. Where subsurface,
laterally moving water is expected to adversely affect an absorption system, a
lateral ground water movement interceptor (LGMI) shall be placed upslope of the
absorption area. The LGMI shall be placed perpendicular to the general slope of
the land. The invert of the LGMI shall extend into, but not through, the
restriction and shall extend for a distance of 10 feet on either side of the
absorption area.

Table 5.4.
Area Requirements for Absorption Trenches.

Percolation
Rate
(Minutes/Inch)

Area Required
(Ft2/100 Gals)

Area Required
(Ft2/Bedroom)

Gravity

Gravity
Gravelless

Low
Pressure
Distribution

Gravity

Gravity
Gravelless

Low Pressure
Distribution

5

110

83

110

165

124

165

10

120

90

120

180

135

180

15

132

99

132

198

149

198

20

146

110

146

218

164

218

25

158

119

158

237

178

237

30

174

131

164

260

195

255

35

191

143

170

286

215

260

40

209

157

176

314

236

264

45

229

172

185

344

258

279

50

251

188

193

376

282

293

55

275

206

206

412

309

309

60

302

227

217

452

339

325

65

331

248

228

496

372

342

70

363

272

240

544

408

359

75

398

299

251

596

447

375

80

437

328

262

656

492

394

85

479

359

273

718

539

409

90

525

394

284

786

590

424

95

575

489

288

862

733

431

100

631

536

316

946

804

473

105

692

588

346

1038

882

519

110

759

645

379

1138

967

569

115

832

707

416

1248

1061

624

120

912

775

456

1368

1163

684

J. Controlled blasting. When rock or
rock outcroppings are encountered during construction of absorption trenches
the rock may be removed by blasting in a sequential manner from the top to
remove the rock. Percolation piping and sewer lines shall be placed so that at
least one foot of compacted clay soil lies beneath and on each side of the pipe
where the pipe passes through the area blasted. The area blasted shall not be
considered as part of the required absorption area.

12VAC5-610-955. Drip dispersal.

A. Drip dispersal applies wastewater in an even and
controlled manner over an absorption area. Drip dispersal system components may
include treatment components, a flow equalization pump tank, a filtration
system, a flow measurement method, supply and return piping, small diameter
pipe with emitters, air/vacuum release valves, redistribution control, and
electromechanical components or controls.

B. Drip dispersal system tubing shall be color coded and
certified by the manufacturer as designed and manufactured for the dispersal of
wastewater. All drip dispersal system tubing shall be equipped with emitters
approved for use with wastewater. For the application of septic tank effluent,
the tubing must have self-cleaning emitters.

1. The minimum linear feet of tubing in the system shall be
one-half of the minimum soil absorption area in square feet.

2. All tubing shall be placed on contour.

3. Except as provided by 12VAC5-613, drip systems
dispersing septic tank effluent shall comply with the requirements of 12VAC5-610-594.
Drip systems dispersing secondary effluent or better require a minimum of six
inches of cover over the tubing. Cover may be achieved by a combination of
installation depth and Group II or Group III soil cover or other approved
material over the drip field.

4. The discharge rate of any two
emitters shall not vary by more than 10% in order to ensure that the effluent
is uniformly distributed over the entire drip field or zone.

5. The emitters shall be evenly spaced along the length of
the drip tubing at not less than six inches or more than 24 inches apart.

6. The system design shall protect the drip emitters and
system from the effects of siphoning or backflow through the emitters.

1. For the dispersal of septic tank effluent, the minimum
soil absorption area for a drip system shall be calculated by multiplying the
trench bottom area required for a low pressure distribution system in Table 5.4
of 12VAC5-610-950 by three.

2. For the dispersal of secondary or better effluent, the
minimum soil absorption area shall be calculated by multiplying the trench
bottom area for pressure distribution systems in accordance with subdivision 10
of 12VAC5-613-80 by three.

3. Landscape linear loading rates shall be considered for
sloping absorption areas. For sites where effluent flow is primarily
horizontal, linear loading rates shall be less than four gallons per day per
linear foot. For sites where the flow is primarily vertical, the linear loading
rates shall be less than 10 gallons per day per linear foot.

4. Air/vacuum release valves shall be located at the high
points of the supply and return manifolds to each zone.

D. All drip dispersal systems shall be equipped with
devices or methods to restrict effluent from draining by gravity to portions of
a zone or laterals lower in elevation. Variable distribution due to gravity
drainage shall be 10% or less within a zone.

E. A minimum of six hours of emergency storage above the
high water alarm in the pump chamber shall be provided. The equalization volume
shall be equal to 18 hours of storage. The equalization volume shall be
measured from the pump off level to the high water alarm level. An audio/visual
alarm meeting the requirements of 12VAC5-610-880 B 8 shall be provided for the
pump chamber.

F. Each drip dispersal zone shall be time-dosed over a
24-hour period. The dose volume and interval shall be set to provide
unsaturated flow conditions. Demand dosing is prohibited. Minimum dose volume
per zone shall be 3.5 times the liquid capacity of the drip laterals in the
zone plus the liquid capacity of the supply and return manifold lines (which
drain between doses) accounting for instantaneous loading and drain back.

1. At each dosing cycle, the system design shall only allow
a full dose volume to be delivered.

2. For design flows greater than 1,000 gallons per day, a
means to take each zone off line separately shall be provided. The system shall
have the capability to bypass each zone that is taken out of service such that
each subsequent dose is dispersed to the next available zone in sequence.

G. Filtration shall be provided to remove suspended solids
and prevent clogging of emitters. The filtration design shall meet the drip
tubing manufacturer's particle size requirements for protection of the emitters
at a flow rate equal to or greater than the rate of forward flushing. Filter
flush water shall be returned to the treatment system at a point where the
residuals and volume of the flush water do not negatively impact the effluent
quality or exceed the hydraulic design capacity of the treatment system.

H. A means for measuring or estimating total flow
dispersed to the soil absorption area and to verify field dosing and field
flushing rates shall be provided.

I. The system shall provide forward field flushing to
achieve scouring velocity as specified by the drip tubing manufacturer. Field
flushing shall occur on a routine schedule to prevent excessive solids
accumulation and clogging. Flush water shall be returned to the treatment
system at a point where the residuals and volume of the flush water do not
negatively impact the effluent quality or exceed the hydraulic design capacity
of the treatment system.

J. Electrical components shall be Underwriters Laboratory
(UL) listed for the intended purpose. The designer shall provide a description
with a schematic diagram of the electrical and control functions in the
operation and maintenance manual. The electrical control equipment shall be
mounted within a National Electrical Manufacturers Association (NEMA) 4X rated
enclosure with a rigid latching door. All switches shall be clearly identified,
and all internal wiring shall be factory installed. All wiring shall be
installed according to applicable electrical safety codes and the
manufacturer's installation schematic.

K. All components in a drip dispersal system shall be
rated to withstand contact with wastewater and recommended for this application
by the manufacturer. All components shall be protected from freezing.

L. The designer of the drip dispersal system shall verify
the dosing rates, the flushing rates, and other parameters critical to the
proper operation of the system at the startup inspection. A summary of the
startup inspection shall be included in the operation and maintenance manual
and shall include, at a minimum, the dosing volume, the forward flow flushing
rate, the pressure head of the system, and verification of proper cycling
between zones.

NOTICE: The following
form used in administering the regulation was filed by the agency. The form is
not being published; however, online users of this issue of the Virginia
Register of Regulations may click on the name of a form with a hyperlink to
access it. The form is also available from the agency contact or may be viewed
at the Office of the Registrar of Regulations, General Assembly Building, 2nd
Floor, Richmond, Virginia 23219.